it was necessary to include one of the vertical terminal 

 shafts used in its construction. These were about 60 

 feet in depth, and thus the much smaller scale of 

 y 4 inch to the foot was used. This variation is not 

 as confusing as might be thought, for the human 

 figures in each model provide an immediate and 

 positive sense of proportion and scale. 



Careful thought was devoted to the internal lighting 

 of the models, as this was one of the critical factors in 

 establishing, so far as is possible in a model, an 

 atmosphere convincingly representative of work 

 conducted solely by artificial light. Remarkable 

 realism was achieved by use of plastic rods to conduct 

 light to the tiny sources of tunnel illumination, such 

 as the candles on the miners' hats in the Hoosac 

 Tunnel, and the gas lights in the Thames Tunnel. 

 Xo overscaled miniature bulbs, generally applied in 

 such cases, were used. At several points where the 

 general lighting within the tunnel proper has been 

 kept at a low level to simulate the natural atmosphere 

 of the work, hidden lamps can be operated by push- 

 button in order to bring out detail which otherwise 

 would be unseen. 



The remainder of the material in the Museum's 

 tunneling section further extends the two major as- 

 pects of tunneling. Space limitations did not permit 

 treatment of the many interesting ancillary matters 

 vital to tunnel engineering, such as the unique prob- 

 lems of subterranean surveying, and the extreme 

 accuracy required in the triangulation and subsequent 

 guidance of the boring in long mountain tunnels; 

 nor the difficult problems of ventilating long workings, 

 both during driving and in service; nor the several 

 major methods developed through the years for 

 driving or constructing tunnels in other than the 

 conventional manner. 1 



' There an- tun important secondary techniques for opening 

 subterranean and subaqueous ways, neither a method truly of 

 tunneling. One of these, of ancient origin, used mainly in the 

 construction of shallow subways and utility ways, is the "cut 

 and cover" system, whereby an open trench is excavated and 



then roofed over. the result is, in effect, a tunnel. The - 



cept "I the Other method was propounded in the early 19th 

 century but only used practically in recent years. This is the 

 "trench" method, a sort of subaqueous equivalent of cut and 

 cover. A trench is dredged in the bed of a body of water, 

 into which prefabricated sections of large diameter tube are 

 lowered, in a continous line. The joints are then sealed by 

 diwts, tin- trench is backlilled over the tube, the end an 

 brought up to dryland portals, tin- water is pumped out, and a 

 subterranean passage results. The Chesapeake Hay Bridge 

 T id (1960-1964) is a recent m • i ■ ► t work of this < harai ter. 



Rock Tunneling 



While the art of tunneling soft ground is of rela- 

 tively recent origin, that of rock tunneling is deeply 

 rooted in antiquity. However, the line of its de- 

 velopment is not absolutely direct, but is more 

 logically followed through a closely related branch 

 of technology — mining. The development of mining 

 techniques is a practically unbroken one, whereas 

 there appears little continuity or relationship between 

 the few works undertaken before about the 18th 

 century for passage through the earth. 



The Egyptians were the first people in recorded 

 history to have driven openings, often of considerable 

 magnitude, through solid rock. As is true of all 

 major works of that nation, the capability of such 

 grand proportion was due solely to the inexhaustible 

 supply of human power and the casual evaluation of 

 life. The tombs and temples won from the rock 

 masses of the Nile Valley are monuments of per- 

 severance rather than technical skill. Neither the 

 Egyptians nor any other peoples before the Middle 

 Ages have left any consistent evidence that they were 

 able to pierce ground that would not support itself 

 above the opening as would firm rock. In Egypt 

 were established the methods of rock breaking that 

 were to remain classical until the first use of gun- 

 powder blasting in the 17th century which formed the 

 basis of the ensuing technology of mining. 



Notwithstanding the religious motives which in- 

 spired the earliest rock excavations, more constant and 

 universal throughout history has been the incentive 

 to obtain the useful and decorative minerals hidden 

 beneath the earth's surface. It was the miner who 

 developed the methods introduced by the early civili- 

 zations to break rock away from the primary mass, 

 and who added the refinements of subterranean sur- 

 veying and ventilating, all of which were later to be 

 assimilated into the new art of driving tunnels of large 

 diameter. The connection is the more evident from 

 the fact that tunnelmen are still known as miners. 



COPPER MINING, B.C. 



Therefore, the first model of the sequence, reflet tint; 

 elemental rock-breaking techniques, depicts a hard- 

 rock copper mine (fig. 1). Due to the absence of 

 specific information about such works during the 

 pre-( Ihristian eras, this model is based on no particu- 

 lar period or locale, but represents in a general way, 

 a mine in the Rio Tinto area of Spain where copper 



206 



BULLETIN 240: CONTRIBUTIONS l'ROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



